Process and apparatus for classifying grinding wheels



mg. 1923. mam

C. E. GiLLETT PROCESS AND APPARATUS FOR CLASSIFIING GRINDING WHEELS Filed March 7, 1919 INVENTOR Patented Dec. 18, 1923. v l I narrate stares aarsnr crates.

CHARLES E. GILLETT, F WORCESTER, MASSACHUSETTS, ASSIGNOR TO NORTON COM PANY, OF WORCESTER, MASSACHUSETTS, A CGRPORATION OF MASSACHUSETTS.

PROCESS AND APPARATUS FOR CLASSIFYING GRINDING WHEELS.

Application filed March 7, 1919. .Serial No 281,303.

To all whom it may concern: 1 cutting edges to the work. That wheel 55 Be it known that 1, CHARLES E. Ginnn'r'r which remains unglazed for the longest time a citizen of,the United States of America, 'is'therefore the more desirable of two which residing at Worcester, in the county of otherwise have the same rate of cutting.-

5 "Worcester and State of Massachusetts,'have In order to obtain a correct classification invented certain new and useful Improvefor a given wheel corresponding with its 60 ments in Processes and Apparatus for actual use in the art, it. is an object of my Classifying Grinding Wheels, of which the invention to classif wheels by means of following is a full,-clear, and exact specltests which are con ucted under conditions fi tib of stress and wheel strain similar to those My invention relates tothe art of classifound in the ordinary operation of the 6 f ing grinding wheels and similar articles. wheel in regular use. 4 lhe methods heretofor proposed for grad- A further object is to provide an appaing wheels made of abrasive grains bonded ratus and a process for grinding a test tool by suitable materials, such as vitrified ce-. by means of the wheel to be classified reramic clays, have involved testing the cording or measuring certain results of the 7 wheels while stationary and not while actoperation and utilizing the data" obtained to ing under true grinding conditions. For identify and classify various essential charexample, wheel manufacturers have tried to acteristics which are inherently associated grade wheels by measuring the depth of with the grindin ability'of the wheel.

penetration of a chisel or flat edged tool Still further oli'ects will be apparent in 7 like a screw driver which is rotated by the following disclosure. power against the wheel or by observing In order that my invention may be fully the fee of the tool when rotated by understood I have illustrated in the drawhand. It has also been roposed to measure ing a diagrammatic representation of the the wear of the tool tlius rotated against essential features of an apparatus adapted 80 the stationary wheel. However, in actual to carry out this method of clamification of operation a grinding wheel rotates at such wheels; a a high velocity that the projecting-grains Figl 1 is an isometricview thereof;

of abrasive, having considerable momentum Figs. 2 and 3 are charts showing curves cut their way deeply through the work and obtained by means of my method and a'pas produce long thick chips of metal, whereas paratus and by which the grinding chara slowly moving abrasive body would acteristics of an abrasive wheel ma b 1 .merely wear down the metal by a frictional termined and the wheel classified.

scratching action of low efficiency and the Two essential attributes of grinding are abrasive grains would break away from the amount of material removed from the so their settings more readily than when rowork being ground and theamount of wear tated rapidly. The result of grinding at of the wheel. I propose to classify wheels this high rate of velocity gives an apparby utilizing these two functions. as measured 40 ent increase in hardness to the wheel. A under actual grinding operations. This microscopic examination of the metal chips method may be carried out by an apparatus as removed by grinding iron shows that the of the type illustrated in the drawing, acabrasive particles act as chisels or cutting cording to which I may measure the detools, if they have sharp edges and have crease'in size-0f the grinding. wheel and a 4.5 not become glazed. If on the other hand value which varies with the decrease in size the grains are dull or have become glazed of the tool or the movementof the work too the particles removed from the metal are towards the wheel. These measurements frequently rounded in shape and show that may be made either as. instantaneous obser considerable heat has been generated, even 'vations or as continuous records. To illusto the extent of forming fused iron globules. trate both of these methods, I have shown a When the grains become "dull. it' is 'necesrecording device for indicating tool wear sary thatthe wheel be dressed or have its and other characteristics associated with the surface renewed by breaking away the grinding action and a micrometer device for grains from the bond and presenting fresh measuring the wheel wear.

In accordance with my invention, I mount the grinding wheel, whose characteristics are to be determined, upon a spindle and to tate it at a standard velocity which is preferably representative of the speed at which such a grinding wheel is ordinarily rotated in actual use. I then grind thereby a tool held against the wheel under constant pressure preferably for a definite period of time and I determine, in accordance with this embodiment of my invention, the decrease in size 'of the wheel and the forward movement of the tool. The difference between these two measurements indicates the amount of the tool removed. As shown in Fig. 1, the wheel 10 may be mounted upon suitable supports 11 for positive rotation by suitable driving means. The tool 12, comprising in this instance a bar of iron, is also mounted preferably on the same standard 11 in a support or carriage 13 which permits the tool to be moved longitudinally against and away from the wheel. While I may traverse the work and the wheel relative one to the other, I have illustrated the tool 12 in this embodiment as being as wide as the wheel, thereby obviating the necessity for such traversing motion as might be required for a narrow tool. The carriage 13 may comprise a rigid hollow member within which the tool 12'slides, the latter being fixed relative thereto in any adjusted position by means of a set screw 14. In order. that the tool 12 may be moved forward as it is ground away the carriage 13 is mounted for longitudinal movement between two pairs of rollers 15 and 16, these rollers being-suitably supported preferably upon the framework 11. The tool 12- may be held in a forward position against the wheel by means of a weight 17 having a cord 18 which passes over a pulley 19 loosely mounted on a shaft 20,this cord 18 being fastened to a pin 21 on the carriage.

In order to obtain measurement of the decrease in size of the grinding wheel during a classification operation, I may provide a micrometer device con'iprising a screw 30 mounted in the arm 31 carried by the support 1.1 in such a position that its lower end 32 may be brought into contact with the rotating wheel by the turning of the screw by means of the head 33. The head 33 is provided with a scale 34 which may be read by means of a pointer 35 projecting upwardly from the arm 31, these graduations being in any suitable dimension or proportion of parts indicating a change in volume of the wheel. In operation. the screw-threaded member 30 may be turned downward until thepoint 32 just touches the wheel and pro duces a spark. A reading for this position is then taken. Any decrease in size of the wheel may be shown by making a similar reading after a period offlrindine. It is to be noted that this construction enables one to obtain an instantaneous measurement of the size of the wheel during rotation thereof.

In order to ascertain the wear on the tool, I may provide a recording mechanism which gives one a continuous portrayal of the grinding action. For this purpose, I provide an arm 40 carrying at its outer end a recordinginstrument such as a pencil 41 and having on its other end a ball 42 engaging a socket in an upright slidable block 43 adjustably fastened to the carriage 13. This adjustment maybe effected by providing the member 43 with a groove 44 and projection 45 cooperating with a correspondingly sha'p'ed projection 46 and a dovetail'slot 47 on the carriage 13, a set screw 48 being pro vided for locking the adjustable member 43 in any desired position.

The arm 40 is.

pivoted on the spindle 49 located adjacent As illustrated, the 'operatii'ig mechanism may.

comprise a motor 52 cooperating through a worm and gear 53 with rollers 54 which frictionally engage the paper 50 and move it at a desired rate.

In operating this device andcarrying out my method, I mount the wheel 10 upon its spindle for rotation at the desired speed. The tool 12 which has been selected for this operation is fastened to the carriage 13 and the adjustable block 43 is moved relative to the carriage until the recording instrument 41 marks the paper 50 at a Zero line 55,.wh'en the tool'12 is held against the grinding face of the wheel by means of the weight 17. The paper 50, which may be suitably marked with cross section lines to indicate. time intervals, is moved at a desired rate corresponding with the spacings on the paper and the grinding wheel 10 is rotated at its normal rate after a measurement has been taken on the micrometer scale 34 to determine the initial size of the wheel. Grinding upon the tool 12 is then started and the device allowed to record the movement of the tool as it is ground away, this -record being shown in the line 56 on'the use graduated in hardness and other physical" characteristics.

The curves shown in Fig. 2 are typical of curves obtained on .the paper 50. e

line 55 in Fig. 1 corresponds With the X-axis and is graduated for definite intervals 0 time. The Y-axis, graduated either in linear measurements or according to some desirable units, indicates the sum of the tool wear and the wheel wear or a value which varies with the forward feed of the tool during grinding. If desired, one may take instantaneous measurements of the wheel wear and plot anew curve, different from the one recorded in the apparatus, to indicate the tool wear alone, or if one uses a recording instrument for determining the wheel wear one may form a third curve from the two recorded curves.

Analysis of the curve A in Fig. 2 shows that the grinding action of the wheel which produced this curve was fairly uniform at first. If this rate had remained uniform, the curve would have been a straight line as indicated by the line B. Due, however, to the abrasive particles ceasing to out effectively, for-any reason, such as dulling, glazing or loading, the curve gradually bent away from this straight line, at first at a slow rate and then, at the approximate location C, at a very rapid rate until the curve became nearly horizontal. This bend or break in the-curve at C indicates the time at which the abrasive power of the wheel became so reduced as to make the wheel unfit for further service without dressing. The curve D indicates a wheel which has a much more rapid cutting ability at first but be comes unservicable much sooner than the wheel A,while the curve E indicates a whee of slow grinding ability but which does not readily glaze. The wheels represented by these separate curves are each e'fiicient in some particular field and it isv one of the purposes of my invention to obtain a quick and accurate classification of these wheels relative to the various grinding operations. If very rapid cutting is desired even at the expense of frequent renewal of the surface of the wheel one corresponding with curve D may best be used, while for general purpose work involving grinding continuously without redressing, a wheel of the characteristics of E may be better than one of the characteristics of D.

1 curve N at the cated at Y,

In order to classify these wheels in accord ance with their hardness of bond and the ability of the wheel to stand up under the strains of grinding, I provide further curves as shown in Fig. 3, which represent values obtained on a set of standard wheels intended for comparison with the wheels under classification. The curve M represents the tool wear or other values corresponding with those recorded by my apparatus and the curve W represents the wheel wear as determined by tests with wheels of all the different grades, the ordinates of the two curves being either of the same or of difierent values and the absclssas representing f grades from soft to hard on any desired scale. Each standard wheel is tested by grindinga standard tool and the tool movement and the wheel wear are determined after a definite period of grinding, the data thus obtained by these separate measurements being plotted to form two separate curves having the same scale for the X-axis, the curves M and W illustrated being merely typical and not necessarily accurate in shape for any particular set of standards. With these standard curves, I may compare any other wheel which is to be classified by means of the measurements obtained in the apparatus described and so determine not only its grade but also other characteristics showing whether the wheel is more or less eificient than another wheel.

Suppose that the standard wheel and the wheel to be classified have been used for grinding the tool for '1 time, and the conditions of classification have been the same. As shown by the recorded characteristics of wheel A, (Fig. 2) the point K corresponding with time T has a tool wear of R, it being noted that the expression tool wear is used broadly to cover either the actual wear of the tool or values which vary with. the wear or grinding action on the tool such as the tool movement described. A corresponding point P which has the same tool wear value R as point K is then located on the curve M in Fig. 3. A perpendicular dropped from the point P interseets'the we will say, grade 5. As shown by curve \V a standard wheel of grade 5 gives a wheel wear of S. If now the wheel wear measurement made by'means of scale 34 gives a value of X then the wheel wearof the unclassified wheel is greater thanthe wear of the standard wheel, and if the point is 10- it is less, thereby showing wheel under consideration is better or poorer than the standard for a given type of grinding operation. If desired, one may utilize the wheel wear instead of the tool wear measurements for determining the grade, in which case the data obtained by means of the micrometer and scale whether the point S and the X-axis at, 1

3% is plotted on the curve W in Fig. 3 and the grade is found to be that represented by the X-value of point S. If the point P is plotted for the wear value R of point K, then its location relative to the curve M determines whether or not the wheel is more or less efficient than the standard wheel.

It is to be noted that the hardness grade of the wheel is determined by the location on one of the two standard curves of a point determined either by measuring the wheel wear or by measurin the tool wear under actual grinding con itions. Furthermore, one need not plot these curves in order to obtain a classification for the wheels since it is sufiicient to compare the measurements of the test with charts made up from data obtained on standard wheels, or one may make comparative tests of the new wheel and another which is supposed to be substan tially the same and is used as a standard. Furthermore, this invention of mine lends itself to making absolute measurements of hardness and grinding characteristics of a wheel in which comparison with other standards is not necessary, the values obtained by means of my apparatus being used directly as grade or classification markings. While the term abrasive wheel has been used throughout this specification it is obvious that theinvention is applicable to classify all similar abrasive articles irrespective of their uses, provided it is feasible to abrade a Wearable tool thereby.

In accordance with this invention I have provided a simple apparatus which may be easily constructed and manipulated and which will determine the grade and classification of a wheel in a reasonable time, and I have provided moreover a method of classification which may be utilized to give the manufacturer and the wheel user more data than heretofore available for determining whatv wheel is best for a given type of grinding work.

ll claim:

1. The method of classifying a grinding wheel comprising the steps of rotating the wheel at a normal grinding velocity, grinding a standard wearable tool thereby under uniform pressure and for a definite period, making successive determinations of the grinding efi'ect of the wheel on the tool as the operation roceeds, measuring the wheel wear produce in the time interval, and from the grinding-characteristics thus observed r wheel comprising means for classifying the wheel by comparison with data obtained with standard wheels.

2. The method of classifying an abrasive wheel comprising the steps of rotating the wheel at a grinding velocity, grinding a standard wearable tool therewith by forcing it against the wheel under constant pressure,

wheel at a normal grinding velocity, grinding a standard wearable tool thereby for a definite period and under a uniform pressure, ascertaining the forward movement of thetool towards the wheel for successive time intervals, measuring the wheel wear during a given time interval, and comparing the data. thus obtained for the different wheels to determine their relative grinding effects upon the tool.

4. A machine for classifying an abrasive supporting and rotating the wheel to be classified at a grinding velocity, a wearable tool, means to sup port the tool and hold it under constant pressure against the grinding wheel, a measuring device mounted on the machine having a member which is manually adjustable into momentary contact with and away from the wheel to indicate the decrease in the size of the wheel during rotation thereof, and means to indicate the forward movement of the tool as it is ground.

5. A. machine for classifying an abrasive wheel comprising means for supporting and rotating the wheel at a grinding velocity, a wearable tool, means to support the tool and hold it under constant'pressure against the grinding wheel, automatic means to draw a graph representing the movement of the tool during the time of the grinding operation and a micrometer screw adjustably mounted upon-the machine to make an instantaneous measurement of the wheel wear during the same period.

Signed at Worcester, Massachusetts, this 28th day of February, 1919.

crninrinsn. GILLETT. 

